제출 #521937

#	제출 시각	아이디	문제	언어	결과	실행 시간	메모리
521937		sofapuden	Mobile (BOI12_mobile)	C++14	100 / 100	835 ms	35176 KiB

mobile

#pragma GCC optimize("Ofast")
#include<bits/stdc++.h>

using namespace std;

int main(){
  ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
  double k;
  int n; cin >> n >> k;
  vector<pair<double,double>> v(n);
  for(auto &x : v)cin >> x.first >> x.second;
  double l = 0, r = 2e9;
  while((r-l) > 0.0001){
    double mid = (l+r)/2.0;
    vector<double> ran1, ran2;
    for(int i = 0; i < n; ++i){
      if(abs(v[i].second) >= mid)continue;
      double z = sqrt(mid*mid-v[i].second*v[i].second);
      while(ran1.size() && max(v[i].first-z,0.0) < ran1.back()){
        ran1.pop_back();
        ran2.pop_back();
      }
      if(ran1.empty() || v[i].first+z > ran2.back()){
        if(ran1.size() && v[i].first-z < ran2.back()){
          ran1.back() = max(0.0,min(v[i].first-z,ran1.back()));
          ran2.back() = min(v[i].first+z,k);
        }
        else{
          ran1.push_back(max(min(v[i].first-z,k),0.0));
          ran2.push_back(min(max(v[i].first+z,0.0),k));
        }
      }
      if(ran1.back() == ran2.back()){
        ran1.pop_back();
        ran2.pop_back();
      }
    }
    if(ran1.empty() || ran1[0] != 0 || ran2.back() != k){
      l = mid;
      continue;
    }
    bool ok = 1;
    for(int i = 1; i < (int)ran1.size(); ++i){
      if(ran2[i-1] < ran1[i]){
        ok = 0;
        break;
      }
      if(ran2[i] == k)break;
    }
    if(ok){
      r = mid;
    }
    else{
      l = mid;
    }
  }
  printf("%.4f\n", l);

}

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